Dealing with non-functioning power folding mirrors on your GMC Sierra can be frustrating, especially when you’ve paid good money for this convenient feature. The good news? You can diagnose and repair the problem yourself in most cases, saving hundreds of dollars compared to dealer prices. This guide walks you through common causes and practical solutions for Sierra mirror problems spanning 2007-2022 models.
Why GMC Sierra Power Folding Mirrors Fail
GMC Sierra mirrors have a notorious weakness that affects thousands of truck owners. If your mirrors aren’t folding properly, you’re not facing a random fluke – you’re experiencing a widespread design issue.
The Plastic Gear Problem
The main culprit behind most GMC Sierra power folding mirror failures is surprisingly simple: weak plastic gears inside the mirror assembly. These thin plastic spur gears crack or break under normal use conditions. You’ll often hear the motor running, but your mirror won’t move when this happens.
When GruvenParts examined thousands of failed mirror assemblies, they discovered these plastic gears simply aren’t strong enough for their purpose. Even minor impacts to your mirror housing can snap these fragile components.
Weak Motors Compound the Issue
Beyond the gear problem, GMC Sierras also suffer from underpowered motors that burn out prematurely. These motors weren’t designed for long-term reliability, creating a perfect storm of failure points in your mirror system.
These issues don’t just affect Sierras – they’re common across GM’s truck and SUV lineup, including Silverados, Yukons, Tahoes, Suburbans, and Escalades from 2007-2022.
Quick Diagnostic Checklist
Before diving into repairs, run through these quick checks to narrow down your problem:
- Can you hear the motor running when you hit the fold button?
- Does one mirror work but not the other?
- Do mirrors move partially before stopping?
- Have you checked if the issue is intermittent or constant?
Your answers will guide which repair path to follow below.
Step-by-Step Troubleshooting Process
1. Check Your Fuses First
Before dismantling anything, always start with the simplest fix – checking your fuses. The power folding mirror system in GMC Sierras relies on three key fuses:
- Driver’s side fuse box: Locate and check Fuse 40 (30A) and Fuse 8 (10A)
- Passenger’s side fuse box: Check Fuse 42
The fuse boxes are located behind removable panels on each side of your dashboard. Even if fuses look good visually, test them with a multimeter for continuity. Hairline cracks aren’t always visible to the naked eye.
2. Test Your Mirror Switch
If your fuses check out, test whether one mirror responds when selecting the other position. For example, if your passenger mirror moves when you’ve selected the driver’s side position on the switch, your problem likely lies in the mirror assembly rather than the switch itself.
A quick way to test this: toggle between mirror positions while operating the folding function. If either mirror responds at any point, you know your switch and wiring are at least partially functional.
3. Clean Corroded Switch Contacts
Intermittent operation often points to dirty or corroded switch contacts. This is a common issue that’s relatively simple to fix:
- Remove the mirror switch by carefully prying around the edges with plastic trim tools
- Inside, you’ll find a rubber contact pad with conductive surfaces
- Clean these contacts using isopropyl alcohol and cotton swabs
- For stubborn corrosion, gently use a pencil eraser on the gold contacts
This simple $3-$8 cleaning job resolves about 80% of intermittent switching problems. Many owners report immediate restoration of full functionality after this cleaning.
4. Perform the Three-Cycle Reset
If your mirrors have been manually moved or act erratically, they might need resynchronization. This free procedure often resolves issues where mirrors don’t fold completely or won’t stay in position:
- Start your Sierra with the engine running
- Make sure the mirror switch is in the center position
- Press the fold button to close mirrors completely
- Press the button again to open them fully
- Repeat this cycle three times total
During the reset process, you should hear a clicking sound. This reset procedure recalibrates the mirror’s internal position sensors and often resolves folding problems without replacing any parts.
5. Identify Gear Failure Symptoms
When you can hear the motor running but see no mirror movement, the plastic drive gear has almost certainly failed. Confirming signs include:
- Motor humming with no visible mirror motion
- Mirror moves partway then stops
- Grinding or clicking sounds during operation
This diagnosis typically means you’ll need to open the mirror assembly to replace components.
6. Test Motor Function
If you suspect motor issues:
- Remove the mirror housing cover by carefully prying with plastic trim tools
- Access the motor connector
- Test for 12 volts at the motor terminals while operating the switch
If voltage is present but the motor doesn’t run, the motor itself has failed and needs replacement.
DIY Repair Options and Costs
Once you’ve identified the issue, you have several repair options at different price points:
Option 1: Dealer Replacement ($700-1,200)
The most expensive but straightforward option is having the dealer replace the entire mirror assembly. However, this approach:
- Costs 5-10 times more than DIY repairs
- Installs the same failure-prone parts that will break again
- Usually isn’t necessary since specific components can be replaced
Option 2: Budget Plastic Gear Replacement ($15-25)
For a temporary fix, you can replace the broken plastic gear with another plastic part:
- Affordable and relatively simple to install
- Requires disassembling the mirror housing
- Only has about a 60% long-term success rate
- Will eventually fail under the same stresses
This approach works well if you’re on a tight budget or plan to sell your truck soon.
Option 3: Metal Gear Upgrade ($150-250)
For a permanent solution, GruvenParts offers a brass spur gear and high-torque motor combination that provides:
- Metal gears many times stronger than OEM plastic parts
- Lifetime warranty on the gear assembly
- 98% success rate based on extensive testing
- Compatibility with 2007-2022 GM trucks
Important note: If upgrading to metal gears, you must use the upgraded motor as well. OEM motors will short out when connected to metal gears due to grounding issues.
Step-by-Step Mirror Disassembly Guide
If you’re tackling the repair yourself, here’s how to access the gear and motor:
Tools You’ll Need:
- Plastic trim removal tools
- T15 Torx driver
- Small Phillips screwdriver
- Needle-nose pliers
- Electrical tape
Disassembly Steps:
- Disconnect the battery – Safety first! Disconnect the negative terminal.
- Remove the mirror glass:
- Tilt the glass toward you
- Insert plastic trim tool at the inner edge
- Carefully pry until the glass pops free
- Disconnect any heating element wires
- Remove the mirror housing:
- Remove visible screws inside mirror housing
- Carefully pry around edges to release clips
- Disconnect electrical connectors
- Access the motor assembly:
- Locate the small motor/gear housing
- Remove retaining screws
- Carefully separate housing halves
- Note the position of gears before removal
- Replace gears and/or motor:
- Remove broken gear carefully
- Install replacement gear in same orientation
- If replacing motor, transfer any position sensors
- Reassemble in reverse order
Preventive Maintenance Tips
To extend the life of your power folding mirrors (whether original or repaired):
- Avoid extreme temperatures when operating mirrors – very cold conditions strain the motors
- Don’t force fold mirrors manually unless absolutely necessary
- Keep mechanisms clean – periodically clean exposed areas with compressed air
- Apply dielectric grease to electrical connections when reassembling
- Address noises immediately – grinding or clicking usually indicates developing problems
Comparison: Repair Options for GMC Sierra Power Folding Mirrors
| Repair Approach | Cost | Difficulty | Durability | Time Required |
|---|---|---|---|---|
| Dealer Replacement | $700-1,200 | None (professional) | 2-3 years (same issue will recur) | 1-2 hours at dealer |
| DIY Plastic Gear | $15-25 | Moderate | 1-2 years | 2-3 hours |
| Metal Gear Upgrade | $150-250 | Moderate-High | 5+ years with lifetime warranty | 3-4 hours |
| Switch Cleaning | $0-8 | Easy | 1-3 years | 30 minutes |
| Fuse Replacement | $3-10 | Very Easy | Permanent (if electrical issue) | 15 minutes |
Real Owner Success Stories
Many Sierra owners have successfully repaired their power folding mirrors:
“After four dealer visits and $800, they still couldn’t fix my mirrors. I found the metal gear upgrade online, spent an afternoon installing it, and two years later they’re still working perfectly.” – Mike S., 2015 Sierra owner
“My mirrors would fold halfway then stop. I tried the three-cycle reset and they’ve been working flawlessly for months now. Can’t believe the dealer wanted $600 for this fix!” – Jennifer T., 2018 Sierra Denali owner
“The plastic gear in my driver’s side mirror broke three times in two years. Finally upgraded to the metal gear kit and haven’t had a problem since. Well worth the investment.” – Carlos R., 2016 Sierra AT4 owner
When To Consider Advanced Diagnostic Tools
If basic troubleshooting doesn’t identify your issue, you might need to check electrical systems more thoroughly. Several NHTSA complaints regarding power accessories in GMC trucks suggest intermittent electrical issues can sometimes affect mirror function.
Consider using an OBD-II scanner with body control module (BCM) capabilities to check for stored codes. Some auto parts stores offer free scanning services if you don’t own the equipment.
The good news is that almost all GMC Sierra power folding mirror issues can be resolved with the steps outlined above. Whether you choose a budget fix or a permanent upgrade, you can restore this convenient feature without breaking the bank.
